Chapter 3 - Section 3.5 - Equations of Lines - Exercise Set - Page 254: 60

a) $y=12000x+18000$ b) 102000 profit after year 7

a) year 1 had 30000 profit year 4 had 66000 profit $(1,30000)$ and $(4,66000)$ are the points $m=(66000-30000)/(4-1)$ $m = 36000/3$ $m=12000$ $y=mx+b$ $30000=12000*1+b$ $30000 = 12000+b$ $18000 = b$ $y=12000x+18000$ b) $y=12000x+18000$ After 7 years, $y=12000x+18000$ $y=12000*7+18000$ $y=84000+18000$ $y=102000$